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The effect of surface wettability on the dielectric properties of contaminated sands Li, Camille

Abstract

The purpose of this study was to investigate the complex dielectric response of the rock/fluid interface and its dependence on surface wettability over the frequency range 100 kHz to 10 MHz. Laboratory experiments were conducted on silica sand and a high surface area silica gel with water-wet, oil-wet and hydrophobic surfaces. A suite of water-wet/oil-wet silica gel mixtures in varying proportions was also used. The dielectric constant and conductivity of samples fully saturated with a 0.001 M NaCl brine were calculated from complex admittance measurements. An inclusion-based effective medium theory (EMT) and the Cole-Cole model were used to interpret the experimental data. The concept of a wetted matrix phase allowed the comparison of measurements from samples with different surface characteristics by removing the effects of disparate porosities and water content from the data. A correlation was found to exist between the surface properties of the sample and both the magnitude and frequency dependence of its dielectric response. Results from the application of the EMT and the Cole-Cole model revealed a tendency for the dielectric constant to decrease and the degree of dispersion to increase with the fraction of oil-wet surface in the sample. Although further studies are needed to more accurately quantify the nature of these relationships, the results presented here suggest that dielectric measurements could provide a useful means of assessing the extent and state of contaminants in porous rocks and soils.

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